The production of polyurethane foams in the presence of small quantities of water in order to utilize the quantity of CO.sub.2 formed in the reaction with the polyisocyanates for the expansion of the foamed plastic is known.
Since even small quantities of water, particularly in association with the conventional activation of foamed plastics formation, lead to the evolution of large quantities of CO.sub.2, only stoichiometrically very small quantities of water are used. The addition of large quantities of water usually leads to unstable, inhomogeneous or mostly unusable, that is, undesirable products of the process.
In DE-OS 4,414,331 and 4,438,409, optionally cellular polyurethanes and/or polyureas are described. These references describe the reaction of film-forming aluminum-phosphate-alkanolamine complexes, present in aqueous solutions, together with polyisocyanates and basic polyols, as well as auxiliary substances and other additives to form fire-resistant polyurethane/polyurea foamed plastics which are of interest technically. Although such formulations, or reaction mixtures, contain large, non-stoichiometric quantities of water which is considerably in excess of the quantities of water usually employed for purposes of expansion.
Characteristic of these processes is the use of substantial quantities of film-forming metal phosphate-alkanolamine complexes in aqueous solutions. Surprisingly, these film-forming metal phosphate-alkanolamine complexes in aqueous solutions can be used for the formation of PU foamed plastics according to the invention, without the large quantities of water thereby brought into the production process which hinders the formation of usable foamed plastics or causes an undesirably vigorous evolution of CO.sub.2 through consumption of the polyisocyanate present.
Until now it could be assumed that the presence of film-forming metal phosphate complexes is necessary for the surprising formation of usable foamed plastics by the above processes. Possibly, this is due to their apparent polymer-like character, or because the metals might have a controlling effect on the isocyanate reaction, or such concentrated solutions of the complexes are, for reasons unknown, particularly suitable for these processes.
Surprisingly, it has now been established that viscous, or concentrated solutions such as, for example, 75% aqueous solutions of sugars, protein hydrolysates, or even other polyhydroxyl compounds can also be used in a similar manner for the production of foamed plastics which are of interest technically, without the concomitant use of organometallic or amine catalysts which are known per se.
By virtue of the present invention, henceforth even water-soluble, so-called renewable raw materials which are insoluble in the previously known conventional PU foam formulations can be used in a very simple manner for the production of foamed plastics having varied technical uses and good biodegradability and/or fire resistance. Examples of the so-called renewable raw materials include, for example, saccharose, water-soluble starches, dextrins, dextrans and similar carbohydrates or hydrolysates obtainable from cellulose or starches, so-called glucose syrups or sugar syrups or even protein-containing solutions.